Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754956Ab3DWF6G (ORCPT ); Tue, 23 Apr 2013 01:58:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:30339 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753750Ab3DWF6E (ORCPT ); Tue, 23 Apr 2013 01:58:04 -0400 Date: Tue, 23 Apr 2013 08:57:44 +0300 From: Gleb Natapov To: Rik van Riel Cc: Peter Zijlstra , Jiannan Ouyang , LKML , Raghavendra K T , Avi Kivity , Ingo Molnar , Marcelo Tosatti , Srikar , "H. Peter Anvin" , "Nikunj A. Dadhania" , KVM , Thomas Gleixner , Chegu Vinod , "Andrew M. Theurer" , Srivatsa Vaddagiri , Andrew Jones , Karen Noel Subject: Re: Preemptable Ticket Spinlock Message-ID: <20130423055743.GB12401@redhat.com> References: <51745650.9050204@redhat.com> <1366631460.4443.3.camel@laptop> <51753289.70406@redhat.com> <1366660147.6454.6.camel@laptop> <517595FA.800@redhat.com> <1366661294.6454.18.camel@laptop> <1366664138.8337.18.camel@laptop> <5175C2D6.9020202@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5175C2D6.9020202@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1589 Lines: 40 On Mon, Apr 22, 2013 at 07:08:06PM -0400, Rik van Riel wrote: > On 04/22/2013 04:55 PM, Peter Zijlstra wrote: > >On Mon, 2013-04-22 at 16:46 -0400, Jiannan Ouyang wrote: > > >>- pv-preemptable-lock has much less performance variance compare to > >>pv_lock, because it adapts to preemption within VM, > >> other than using rescheduling that increase VM interference > > > >I would say it has a _much_ worse worst case (and thus worse variance) > >than the paravirt ticket implementation from Jeremy. While full > >paravirt ticket lock results in vcpu scheduling it does maintain > >fairness. > > > >If you drop strict fairness you can end up in unbounded starvation > >cases and those are very ugly indeed. > > If needed, Jiannan's scheme could easily be bounded to prevent > infinite starvation. For example, we could allow only the first > 8 CPUs in line to jump the queue. > > However, given the way that virtual CPUs get scheduled in and > out all the time, I suspect starvation is not a worry, and we > will not need the additional complexity to deal with it. > FWIW RHEL6 uses unfair spinlock when it runs as a guest. We never got reports about problems due to this on any scale. > You may want to play around with virtualization a bit, to get > a feel for how things work in virt land. > > -- > All rights reversed -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/